Novel Method for Monitoring the Electrochemical Capacitance by In Situ Impedance Spectroscopy as Indicator for Particle Cracking of Nickel-Rich NCMs: Part II. Effect of Oxygen Release Dependent on Particle Morphology

Abstract

Nickel-rich NCMs (LiMO2, with M = Ni, Co, and Mn) are increasingly commercialized as cathode active materials for lithium-ion batteries due to their high specific capacity. However, the available capacity is limited due to their structural instability at high state of charge, causing the formation of a resistive surface layer upon release of lattice oxygen, observed at different upper cutoff potentials depending on the NCM composition. To understand the impact of this instability, the correlation of oxygen release, capacity fading, and particle cracking was investigated as a function of state of charge for three nickel-rich NCMs, differing either in composition (i.e., in transition metal ratio) or in morphology (i.e., in primary crystallite size). First, the onset of the release of lattice oxygen was identified by on-line electrochemical mass spectrometry (OEMS). In electrochemical cycling experiments, the NCM capacitance was tracked in situ by impedance spectroscopy (EIS) using a micro-reference electrode while the upper cutoff potential was increased every third cycle stepwise from 3.9 V to 5.0 V. Hereby, the effect of the degree of delithiation on the discharge capacity and on the particle integrity (tracked via its surface area) was examined, both for poly- and single-crystalline NCMs.

Low-cobalt active cathode materials for high-performance lithium-ion batteries: synthesis and performance enhancement methods

“…The lattice oxygen release exacerbates the particle cracking related issue, which deteriorates the capacitive as well as cycling performance of Ni-rich cathodes. 105,106 Cation doping and interface engineering are two of the efficient strategies to prevent the lattice oxygen escape. 100,107,108…”

“…The lattice oxygen release exacerbates the particle cracking related issue, which deteriorates the capacitive as well as cycling performance of Ni-rich cathodes. 105,106 Cation doping and interface engineering are two of the efficient strategies to prevent the lattice oxygen escape. 100,107,108 5 Strategies to improve the electrochemical performance High Ni-content NCMs, specically NCM-811, would be a potential cathode material for the production of commercial high energy Li-ion batteries only if the issues can be addressed rationally.…”

Operando odd random phase electrochemical impedance spectroscopy as a promising tool for monitoring lithium-ion batteries during fast charging

“…The state-ofthe-art monitoring approaches are mostly based on conventional parameters i.e., voltage, current and temperature, and assisted by the Coulomb counting method, however it becomes insufficient in more complex usage conditions [53]. Applying the fast-charging in a mismatched SoC region (i.e., low or high SoC region) leads to accelerated aging effects on batteries such as the destabilization of the lattice structure, the release of lattice oxygen, side (electro)chemical reactions and excessive heat generation etc, leading to a rapid degradation of the batteries and safety hazards [54][55][56][57]. Many researchers thus are shifting their focus to more physics-oriented strategies providing direct insights towards the battery materials [58].…”

Microcracking of Ni-rich layered oxide does not occur at single crystal primary particles even abused at 4.7 V

“…There are many reasons of the capacity loss due to intrinsic properties of CAMs such as oxygen releasing and surface reconstruction leading to electrochemical inactive phase, [2][3][4] particle cracking leading to electronically isolated phase, [5][6][7] and Li-Ni mixing leading to Li-site blockage. [8][9][10][11][12] In this work, we focus on the particle cracking phenomenon having a controversial and important question how and where the origin of the cracking occurs at the CAMs, whether it started at the primary crystalline particle or at grain boundaries. 10,13 We showed the comprehensive investigation of both polycrystalline (Poly-NMC) and single-crystal LiNi 0.8 Mn 0.1 Co 0.1 O 2 (SC-NMC) as CAMs with graphite anode at an n/p ratio of 1.1 in practical full-cell 18 650 batteries in many aspects, including the effect of the formation protocols, long-term stability, and high voltage stability with online gas evolution.…”

“…There are many reasons of the capacity loss due to intrinsic properties of CAMs such as oxygen releasing and surface reconstruction leading to electrochemical inactive phase, 2–4 particle cracking leading to electronically isolated phase, 5–7 and Li–Ni mixing leading to Li-site blockage. 8–12…”